We report our recent experience of a rare case of a benign mesenchymoma in the mediastinum. A 24-year-old man was admitted to our hospital with an abnormal shadow on chest X-ray. A chest computerized tomography scan and magnetic resonance imaging showed an anterior mediastinal mass along the right border of the pericardium. The tumor was surgically resected. It was yellow on the surface, 12.5 x 10.0 x 3.8 cm in size, and 230 g in weight. The histopathological diagnosis was a benign mesenchymoma. The postoperative course was uneventful. A search of the literature revealed that a benign mesenchymoma in the mediastinum is extremely rare. It seems to be difficult to reach a definitive diagnosis preoperatively. Surgical resection can confirm the diagnosis, and is curative.